Meiosis Key Concepts PDF

Meiosis Key concepts review Sexual Reproduction: Formation of Gametes Why are we not Clones? Somatic cells reproduce by mitosis, the new daughter cells are genetic copies of the parent cells Asexual reproduction is reproduction that requires only one parent and produces genetical...

Meiosis Key concepts review Sexual Reproduction: Formation of Gametes Why are we not Clones? Somatic cells reproduce by mitosis, the new daughter cells are genetic copies of the parent cells Asexual reproduction is reproduction that requires only one parent and produces genetically identical offspring (ex.bacteria) If humans only reproduced via mitosis we would be exact clones of ourselves Humans reproduce through sexual reproduction - which involves two parents and leads to genetically distinct offspring terminology in sexual reproduction Sexual reproduction - fusion of male and female reproductive cells Gametes - a male or female reproductive cell that is haploid n = 23 ○ Male gamete - sperm Female gamete - egg cell OR ovum Zygote - cell formed by fusion of two gametes, diploid with 2n chromosomes (n chromosomes from ♀ and n from ♂) Fertilization - joining of male and female haploid gametes to produce a zygote Haploid - cell that contains half the number of chromosomes as the parent cell Diploid - cell that contains pairs of homologous chromosomes What are two key outcomes of meiosis??? Why is this important? Brainstorm…. Meiosis - producing haploid gametes different from the parent The process that produces gametes with a haploid number of chromosomes is called meiosis. It has two outcomes: ○ genetic reduction: a form of cell division that produces daughter cells with half the number of chromosomes of the parent cell ○ genetic recombination: the products of meiosis have different combinations of alleles Haploid and diploid cells in sexual reproduction The zygote has the same number of chromosomes as a somatic cell. To achieve this, each gamete only carries one set of homologous chromosomes. A cell with one set is haploid (n); a cell with two sets is diploid (2n). The human diploid number is 2n = 46. Gametes have half the number of chromosomes as the parent cells MEIOSIS Meiosis involves two complete cycles of four phases. Notice that each cell contains some chromosomes from the mother (yellow), some chromosomes from the father (blue), and some chromosomes with segments that have been exchanged (yellow and blue). Magnification: 200x Gamete formation in animals Spermatogenesis is the process that produces sperm in male animals; oogenesis produces eggs in females. In males, the spermatogonia reproduce by mitosis and then meiosis, starting at puberty. In females, the oogonia reproduce by mitosis before birth. They begin meiosis but stop at prophase I. Each month after puberty, one cell completes meiosis. However, the cytoplasm is unequally distributed, and only one cell matures, not four. Spermatogenesis and oogenesis How does the process of meiosis contribute to genetic diversity??? Brainstorm…. The importance of meiosis for genetic variation During meiosis, genetic variation is ensured in two ways: independent assortment and crossing over. In a process called independent assortment, gametes are created that carry different combinations of maternal and paternal chromosomes. This occurs during metaphase I, when each homologous chromosome is randomly oriented towards one of the poles. This alone can produce over 8 million different chromosome combinations. The importance of meiosis for genetic variation In a process called crossing over, genetic material between maternal and paternal chromosomes is exchanged. This occurs during prophase I in which non-sister chromatids exchange genetic material in multiple sections.